Semipermeable high density polyethylene(HDPE) membranes were prepared by photoinduced grafting of acrylic acid(AA) onto HDPE films. The reverse osmosis characteristics of HDPE-g-AA membranes of different graft yields were evaluated. These properties were found to very with the composition of the graft copolymer membrane; most properties were found to be a linear function of the graft yield. As the graft yield was increased, the water flux and the water content were increased but the salt rejection was decreased, and these were related to the effect of feed solution concentration.